1. Field of the Invention
The present invention relates generally to an improved push-in interbody (for placement at least in part between adjacent vertebral bodies) spinal fusion implant for the immobilization of vertebrae. The present invention is directed to push-in implants only and not to threaded implants. In particular, the invention relates to a push-in spinal fusion implant that is selectively directionally expandable and which specifically has height raising capabilities that are utilized once the implant is initially positioned. More particularly, the invention relates to a push-in implant having arcuate portions of upper and lower members that in a first, collapsed, or insertion position are angled to one another and form at least a portion of a frusto-conical shape, or of a cylinder split along a horizontal plane through its mid-longitudinal axis wedging the upper half from the lower half by an inclined plane, along a substantial portion of the length of the implant.
2. Description of the Related Art
Push-in spinal fusion implants having upper and lower arcuate portions adapted for placement in contact with adjacent vertebral bodies are known in the related art. Such a push-in spinal fusion implant was invented by Michelson and is disclosed in U.S. Pat. No. 5,593,409, filed Feb. 17, 1995, which is hereby incorporated by reference.
Lordotic, frusto-conical, or tapered, push-in spinal fusion implants are also known in the art. By way of example, Michelson has invented such implants as disclosed in U.S. application Ser. No. 08/484,928, filed Jun. 7, 1995, which is hereby incorporated by reference.
Expandable fusion implants are known in the related art. The first expandable spinal fusion (allowing for the growth of bone from vertebral body to vertebral body through the implant) implant was invented by Michelson and is disclosed in U.S. Pat. No. 5,776,199, filed Jun. 28, 1988, which is hereby incorporated by reference.
Lordotic, frusto-conical, or tapered, spinal fusion implants have the advantage of restoring or enhancing spinal lordosis. Push-in spinal fusion implants offer the advantage of being easily positioned in the implantation space and of having excellent fastening or holding features. Expandable fusion implants offer the advantage of allowing for the placement of a potentially larger implant through a smaller opening in a patient's body. Selective expansion along a single direction, (e.g. vertically only when correctly installed) offers the advantage of increasing the height of the implant and therefore the distraction of the disc space, but without a concomitant increase in the width of the implant.
There exists a need for an artificial interbody spinal fusion implant providing for all of the aforementioned advantages in combination.